The present invention relates to the fields of oncology and diagnostic testing, and more particularly to methods for cancer screening and for predicting and monitoring chemotherapy treatment responses, cancer recurrence or the like.
Insulin-like growth factor (IGF-1) is a 7.5 kD polypeptide that circulates in plasma in high concentrations and is detectable in most tissues. IGF-1, which is structurally similar to insulin, stimulates cell differentiation and cell proliferation, and is required by most mammalian cell types for sustained proliferation. These cell types include, among others, human diploid fibroblasts, epithelial cells, smooth muscle cells, T lymphocytes, neural cells, myeloid cells, chondrocytes, osteoblasts, and bone marrow stem cells.
The first step in the transduction pathway leading to IGF-1-stimulated cellular proliferation or differentiation is binding of IGF-1 or IGF-2 (or insulin at supraphysiological concentrations) to the IGF-1 receptor (IGF-1R). The IGF-1R belongs to the family of tyrosine kinase growth factor receptors (Ullrich et al., Cell 61: 203-212, 1990), and is structurally similar to the insulin receptor (Ullrich et al., EMBO J. 5: 2503-2512, 1986).
Epidemiological studies suggest that high end normal levels of IGF-1 increase the risk of cancers such as lung, breast, prostate and colorectal, compared to individuals with IGF-1 levels at the low end of normal. Further, there is considerable evidence for a role for IGF-1 and/or IGF-1R in the maintenance of tumor cells in vitro and in vivo. IGF-1R levels are elevated in tumors of lung (Kaiser et al., J. Cancer Res. Clin. Oncol. 119: 665-668, 1993; Moody et al., Life Sciences 52: 1161-1173, 1993; Macauley et al., Cancer Res., 50: 2511-2517, 1990), breast (Pollak et al., Cancer Lett. 38: 223-230, 1987; Foekens et al., Cancer Res. 49: 7002-7009, 1989; Arteaqa et al., J. Clin. Invest. 84: 1418-1423, 1989), prostate and colon (Remaole-Bennet et al., J. Clin. Endocrinol. Metab. 75: 609-616, 1992; Guo et al., Gastroenterol. 102: 1101-1108, 1992). Deregulated expression of IGF-1 in prostate epithelium leads to neoplasia in transgenic mice (DiGiovanni et al., Proc. Nat'l. Acad. Sci. USA 97: 3455-3460, 2000). In addition, IGF-1 appears to be an autocrine stimulator of human gliomas (Sandberg-Nordqvist et al., Cancer Res. 53 (11): 2475-78, 1993), while IGF-1 has been shown to stimulate the growth of fibrosarcomas that overexpress IGF-1R (Butler et al., Cancer Res. 58: 3021-3027, 1998). For a review of the role IGF-1/IGF-1R interaction plays in the growth of a variety of human tumors, see Macaulay, Br. J. Cancer, 65: 311-20, 1992.
Using antisense expression vectors or antisense oligonucleotides to the IGF-1R RNA, it has been shown that interference with IGF-1R leads to inhibition of IGF-1-mediated cell growth (see, e.g., Wraight et al., Nat. Biotech. 18: 521-526, 2000). Growth can also be inhibited using peptide analogues of IGF-1 (Pietrzkowski et al., Cell Growth & Diff. 3: 199-205, 1992; Pietrzkowski et al., Mol. Cell. Biol. 12: 3883-3889, 1992), or a vector expressing an antisense RNA to the IGF-1 RNA (Trojan et al., Science 259: 94-97, 1992). In addition, antibodies to IGF-1R (Arteaga et al., Breast Canc. Res. Treatm. 22: 101-106, 1992; and Kalebic et al., Cancer Res. 54: 5531-34, 1994), and dominant negative mutants of IGF-1R (Prager et al., Proc. Nat'l Acad. Sci. USA 91: 2181-85, 1994; Li et al., J. Biol. Chem. 269: 32558-2564, 1994; Jiang et al., Oncogene 18: 6071-6077, 1999), an reverse the transformed phenotype, inhibit tumorigenesis, and induce loss of the metastatic phenotype.
IGF-1 is also important in the regulation of apoptosis. Apoptosis, which is programmed cell death, is involved in a wide variety of developmental processes, including immune and nervous system maturation. In addition to its role in development, apoptosis also has been implicated as an important cellular safeguard against tumorigenesis (Williams, Cell 65: 1097-1098, 1991; Lane, Nature 362: 786-787, 1993). Suppression of the apoptotic program may contribute to the development and progression of malignancies.
IGF-1 protects from apoptosis by cytokine withdrawal in IL-3-dependent hematopoietic cells (Rodriguez-Tarduchy, G. et al., J. Immunol. 149: 535-540, 1992), and from serum withdrawal in Rat-1/mycER cells (Harrington, E. et al., EMBO J. 13:3286-3295, 1994). The demonstration that c-myc driven fibroblasts are dependent on IGF-1 for their survival suggests that there is an important role for the IGF-1 receptor in the maintenance of tumor cells by specifically inhibiting apoptosis, a role distinct from the proliferative effects of IGF-1 or IGF-1R.
The protective effects of IGF-1 on apoptosis are dependent upon having IGF-1R present on cells to interact with IGF-1 (Resnicoff et al., Cancer Res. 55: 3739-41, 1995). Support for an anti-apoptotic function of IGF-1R in the maintenance of tumor cells was also provided by a study using antisense oligonucleotides to the IGF-1R that identified a quantitative relationship between IGF-1R levels, the extent of apoptosis and the tumorigenic potential of a rat syngeneic tumor (Rescinoff et al., Cancer Res. 55: 3739-3741, 1995). It has been found that overexpressed IGF-1R protects tumor cells in vitro from etoposide-induced apoptosis (Sell et al., Cancer Res. 55: 303-06, 1995) and, even more dramatically, that a decrease in IGF-1R levels below wild type levels caused massive apoptosis of tumor cells in vivo (Resnicoff et al., Cancer Res. 55: 2463-69, 1995).
Some studies suggest that expression levels of IGF-1R correlate with clinical outcome. In tumor models, IGF-1R modulates cell proliferation, survival and metastasis and induces resistance to targeted therapies. Inhibition of IGF-1R significantly increases the activity of cytotoxic agents (Cohen, B. e al., Clin. Cancer Res. 11(5): 2063-73). Inhibition of IGF-1R signaling thus appears to be a promising strategy for the development of novel cancer therapies.
Malignant tumors of epithelial tissues are the most common form of cancer and are responsible for the majority of cancer-related deaths. Because of progress in the surgical treatment of these tumors, mortality is linked increasingly to early metastasis and recurrence, which is often occult at the time of primary diagnosis (Racila et al., Proc. Nat'l Acad. Sci. USA 95:4589-94, 1998; Pantel et al., J. Nat'l Cancer Inst 91(13): 1113-24, 1999). For example, the remote anatomical location of some organs makes it unlikely that tumors in those organs will be detected before they have invaded neighboring structures and grown to larger than 1 cm. Even with respect to breast cancers, 12-37% of small tumors of breast cancer (<1 cm) detected by mammography already have metastasized at diagnosis (Chadha M. et al., Cancer 73(2): 350-3, 1994.
Circulating tumor cells (“CTCs”) are cells of epithelial origin that are present in the circulation of patients with different solid malignancies. They are derived from clones of the primary tumor and are malignant. (See Fehm et al., Clin. Cancer Res. 8: 2073-84, 2002.) Evidence has accumulated in the literature showing that CTCs can be considered an independent diagnostic for cancer progression of carcinomas (Beitsch & Clifford, Am. J. Surg. 180(6): 446-49, 2000 (breast); Feezor et al., Ann. Oncol. Surg. 9(10): 944-53, 2002 (colorectal); Ghossein et al., Diagn. Mol. Pathol. 8(4): 165-75, 1999 (melanoma, prostate, thyroid); Glaves, Br. J. Cancer 48: 665-73, 1983 (lung); Matsunami et al., Ann. Surg. Oncol. 10(2): 171-5, 2003 (gastric); Racila et al., 1998; Pantel et al., 1999).
Detection and enumeration of circulating tumor cells is important for patient care for a number of reasons. They may be detectable before the primary tumor, thus allowing early stage diagnosis. They decrease in response to therapy, so the ability to enumerate CTCs allow one to monitor the effectiveness of a give therapeutic regimen. They can be used as a tool to monitor for recurrence in patients with no measurable disease in the adjuvant setting. For example, CTC were found to be present in 36% of breast cancer patients 8-22 years after mastectomy, apparently from micrometastases (deposits of single tumor cells or very small clusters of neoplastic cells). Meng et al., Clin. Can. Res. 1024): 8152-62, 2004.
In addition, CTCs may be used to predict progression-free survival (PFS) and overall survival (OS), as the presence/number of circulating tumor cells in patients with metastatic carcinoma has been shown to be correlated with both PFS and OS. See e.g., Cristofanilli et al., J. Clin. Oncol. 23(1): 1420-1430, 2005; Cristofanilli et al., N. Engi. J. Med. 351(8): 781-791, 2004.
However, there remains a need for rapid and reliable assays that are more sensitive than mere detection of CTCs.